736
FXUS66 KMTR 210822
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
122 AM PDT MON JUL 21 2025
..NEW SHORT TERM, LONG TERM, CLIMATE
KEY MESSAGES
UPDATED AT 1221 AM PDT MON JUL 21 2025
- BELOW NORMAL TEMPERATURES CONTINUE THROUGH THE WEEK.
- LOCALIZED ELEVATED FIRE WEATHER THREAT FOR THE EAST BAY HILLS
MONDAY DUE TO GUSTY ONSHORE WINDS.
- GUSTY WINDS RETURN LATE TONIGHT AND CONTINUE THROUGH MONDAY
NIGHT ALONG THE COAST, RIDGETOPS, AND MOUNTAIN GAPS/PASSES.
SHORT TERM
ISSUED AT 1221 AM PDT MON JUL 21 2025
(TODAY AND TONIGHT)
THE MARINE LAYER IS DEEPENING AS STRONG ONSHORE WINDS FUNNEL
THROUGH INLAND GAPS AND PASSES. ALTAMONT PASS IS REPORTING WSW
WINDS GUSTING TO NEAR 50 MPH. FORTUNATELY THE RELATIVE HUMIDITY
IS QUITE HIGH TONIGHT, KEEPING FIRE DANGER SUPPRESSED. THE SFO-
SAC GRADIENT WAS +3.4 MB AT MIDNIGHT, ON A DECREASING TREND. THAT
SHOULD ALLOW THE WINDS TO EASE THROUGH THE MORNING HOURS BEFORE
THE TYPICAL DIURNAL GRADIENT REBUILDS THIS AFTERNOON. THE WRF
ENSEMBLE MEAN BUILDS THE GRADIENT BACK UP TO +4.3 MB LATE
AFTERNOON/EARLY EVENING WHICH SHOULD BRING SIMILAR STRENGTH WIND
GUSTS THROUGH EARLY TUESDAY MORNING. THE DEEP MARINE LAYER, HIGH
RELATIVE HUMIDITY AND STRONG ONSHORE WINDS WILL ENHANCE OROGRAPHIC
LIFT ALONG THE COASTAL MOUNTAINS, AND THERE'S A GOOD CHANCE FOR
DRIZZLE DURING THE MORNING COMMUTE ALONG HWY-1 AND THE NORTHERN
REACHES OF I-280/HWY-101. OTHERWISE IT WILL BE COOLER THAN
YESTERDAY, WITH MEAGER CLEARING IN THE AFTERNOON AND MAX
TEMPERATURES 5-15 DEGREES BELOW NORMAL.
LONG TERM
ISSUED AT 1221 AM PDT MON JUL 21 2025
(TUESDAY THROUGH SUNDAY)
IN SHORT, THE COOL TROUGHING PATTERN IS HERE TO STAY. AT 500 MB, A
POSITIVELY TILTED TROUGH WILL LIKELY SPAWN A CUT-OFF LOW
WEDNESDAY WHICH WILL THEN LINGER A FEW DAYS BEFORE BEING PICKED UP
BY A MORE ROBUST TROUGHING PATTERN THIS WEEKEND. IN THE MEDIUM
TERM, THIS WILL LEAD TO A RELAXED PRESSURE GRADIENT AND PRETTY
BENIGN CONDITIONS THROUGH THE WORK WEEK. THE 850 MB TEMPERATURE
WAS LAST MEASURED AT NEAR THE 75TH PERCENTILE FOR THIS TIME OF
YEAR (21.8 C). AS THE TROUGH DEVELOPS THIS BENCHMARK WILL FALL,
AND THERE IS A 90% CHANCE THAT IT STAYS BELOW THE 25TH PERCENTILE
(16.5 C) FROM TUESDAY - THURSDAY. THAT MEANS COOL, CLOUDY WEATHER
FOR THOSE IN THE MARINE LAYER AND CONTINUED COMFORTABLE CONDITIONS
FOR THOSE FURTHER INLAND. LATER IN THE WEEK, A HIGH PRESSURE
RIDGE WILL GRADUALLY BUILD OVER THE DESERT SW. THIS WILL BRING A
HEAT WAVE TO THE OUR NEIGHBORING STATES, AND NWS TUSCON IS
ADVERTISING A 90% CHANCE OF TEMPERATURES HITTING 105 DEGREES IN
THEIR HOME CITY NEXT SUNDAY (7/27). THERE IS NO INDICATION THAT
THIS RIDGE WILL MOVE ANYWHERE NEAR THE BAY AREA, BUT THE GRADIENT
WILL INCREASE SUBSTANTIALLY BETWEEN OUR DEEPENING TROUGH OFFSHORE
AND THE BUILDING RIDGE TO OUR SE. THIS PATTERN WILL SUPPORT 500 MB
WINDS UP TO 50 KTS FROM THE SW, AND SHOULD BRING ANOTHER ROUND OF
BREEZY SURFACE WINDS NEXT WEEKEND. THIS PROLONGED COOL PERIOD IS
HELPING SUPPRESS WILDFIRE POTENTIAL AND THE ENERGY RELEASE
COMPONENT IS EITHER BELOW AVERAGE OR FORECAST TO FALL BELOW
AVERAGE THIS WEEK FOR ALL REGIONS ACROSS THE BAY AREA AND CENTRAL
COAST.
AVIATION
(06Z TAFS)
ISSUED AT 952 PM PDT SUN JUL 20 2025
MVFR-IFR STRATUS COVERS THE COAST SOUTH OF BODEGA BAY, AND COMES
INLAND INTO THE SONOMA COUNTY VALLEYS, THROUGH THE GOLDEN GATE INTO
THE EAST BAY, AND ACROSS THE MONTEREY BAY, DOWN THE SALINAS VALLEY,
AND INTO THE GILROY-HOLLISTER REGION. STRATUS COVERAGE IS EXPECTED
TO EXPAND THROUGH THE NIGHT WITH MODERATE CONFIDENCE IN STRATUS
IMPACTS IN THE NORTH BAY VALLEYS, SOMEWHAT LOWER AT STS. RECENT
OVERPERFORMANCE OF THE STRATUS LAYERS COMPARED TO MODEL OUTPUT HAS
MADE THE FORECAST RATHER DIFFICULT, BUT THE BEST INDICATION IS THAT
STRATUS WILL RETREAT TO THE IMMEDIATE COASTAL REGION THROUGH MONDAY
MORNING, WITH BREEZY AND GUSTY ONSHORE FLOW DEVELOPING MONDAY
AFTERNOON. LOW CONFIDENCE IN STRATUS CLEARING AT OAK AND MRY AS
ONSHORE FLOW AND A ROBUST MARINE LAYER COULD KEEP CEILINGS AT BOTH
TERMINALS THROUGH THE DAY. STRATUS WILL BEGIN TO DEVELOP INLAND
MONDAY EVENING.
VICINITY OF SFO... MVFR-IFR STRATUS CONTINUES TO IMPACT THE TERMINAL
OVERNIGHT INTO MONDAY MORNING. LOW CONFIDENCE IN STRATUS CLEARING
TIME ACROSS THE TERMINAL AREA AS STRATUS HAS OVERPERFORMED THE
MODELS OVER THE LAST FEW DAYS, BUT EXPECT SEVERAL HOURS OF VFR
CONDITIONS IN THE AFTERNOON. LOWER CONFIDENCE IN CLEARING AT OAK.
BREEZY ONSHORE WINDS RETURN TO THE TERMINAL MONDAY AFTERNOON AND
EVENING, DIMINISHING AS THE STRATUS RETURNS TO THE TERMINAL AREA.
GREATEST CONFIDENCE IS FOR STRATUS TO RETURN TO THE NORTH OF THE
TERMINAL.
SFO BRIDGE APPROACH... LOWER CONFIDENCE IN STRATUS IMPACTS,
WITH LATER ARRIVAL TIMES THAN THE TERMINAL. OTHERWISE SIMILAR TO SFO.
MONTEREY BAY TERMINALS... IFR-LIFR CEILINGS CONTINUE OVERNIGHT.
STRATUS RETREATS TO THE IMMEDIATE COAST LATE MONDAY MORNING WITH
MODERATE TO HIGH CONFIDENCE THAT MRY IS SOCKED IN THROUGH THE END OF
THE TAF PERIOD. BREEZY ONSHORE FLOW RESUMES MONDAY AFTERNOON.
MARINE
(TONIGHT THROUGH NEXT SATURDAY)
ISSUED AT 821 PM PDT SUN JUL 20 2025
MODERATE BREEZES TO NEAR-GALE FORCE GUSTS ARE EXPECTED TONIGHT
INTO MONDAY, RESULTING IN HAZARDOUS BOATING CONDITIONS FOR
SMALLER VESSELS IN THE NORTHERN SAN FRANCISCO AND SAN PABLO BAYS
AND ACROSS THE NORTHERN OUTER WATERS. STRONG BREEZES WILL ALSO
PERSIST INTO THE PRE- DAWN HOURS ON MONDAY ACROSS THE BIG SUR
COASTLINE. SLIGHT TO MODERATE SEAS PERSIST THROUGH THE REMAINDER
OF THE FORECAST PERIOD. WINDS EASE SOME THROUGH TUESDAY, EXCEPT
ACROSS SOUTHERN PORTIONS OF THE BIG SUR COAST, WHERE STRONG
NORTHWEST BREEZES PERSIST. OTHERWISE, REDUCED VISIBILITY SHOULD
BE ANTICIPATED DURING THE MORNING HOURS DUE TO FOG AND DRIZZLE.
CLIMATE
ISSUED AT 1221 AM PDT MON JUL 21 2025
THIS SUMMER HAS BEEN COOLER THAN AVERAGE AND THAT TREND WILL
CONTINUE FOR AT LEAST ANOTHER WEEK. I DECIDED IT WAS A GOOD TIME
TO ADD A CLIMATE SECTION HERE TO COMPARE JUST HOW DIFFERENT THIS
SUMMER HAS BEEN THAN LAST YEAR. I CREATED A SIMPLE HEAD-TO-HEAD
SCORING SYSTEM TO ADD DAYS ABOVE/BELOW NORMAL WEIGHTED BY HOW FAR
ABOVE/BELOW NORMAL THEY WERE. FOR EXAMPLE, IF THE MAXIMUM
TEMPERATURE WAS 2 DEGREES BELOW NORMAL ON SATURDAY AND 3 DEGREES
ABOVE NORMAL ON SUNDAY, THE SCORE WOULD BE 2-3. I FOCUSED ON MAX
TEMPERATURE AT SAN JOSE FROM JUNE 1 - JULY 20. METEOROLOGICAL
SUMMER STARTS JUNE 1ST AND SAN JOSE IS A GOOD MIXTURE OF SOME
MARINE LAYER INFLUENCE AND INLAND HEAT DEPENDING ON THE DAY.
AGAIN, I JUST MADE THIS SCORING SYSTEM UP TONIGHT, SO HOPEFULLY IT
MAKES SENSE. THE RESULTS ARE PRETTY INTERESTING, PARTICULARLY
WHEN COMPARED WITH LAST YEAR.
2025: COLD: 168, WARM: 36
2024: COLD: 30, WARM: 302
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR SF BAY N OF
BAY BRIDGE.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM PDT THIS
EVENING FOR MRY BAY-PIGEON PT TO PT PINOS 0-10 NM-PT PINOS
TO PT PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT THIS MORNING FOR PT ARENA TO
PT REYES 0-10 NM-PT ARENA TO PT REYES 10-60 NM.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...DIALH
MARINE...DIALH
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